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unified encoding types

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Yann Collet
2016-07-23 16:31:49 +02:00
parent 571a59034a
commit f8e7b5363f
5 changed files with 61 additions and 71 deletions
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zstd_compression_format.md
+11 -11
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@@ -437,19 +437,19 @@ Header is in charge of describing how literals are packed.
It's a byte-aligned variable-size bitfield, ranging from 1 to 5 bytes,
using little-endian convention.
| BlockType | sizes format | regenerated size | [compressed size] |
| --------- | ------------ | ---------------- | ----------------- |
| 2 bits | 1 - 2 bits | 5 - 20 bits | 0 - 18 bits |
| EncodingType | sizes format | regenerated size | [compressed size] |
| ------------ | ------------ | ---------------- | ----------------- |
| 2 bits | 1 - 2 bits | 5 - 20 bits | 0 - 18 bits |
In this representation, bits on the left are smallest bits.
__Block Type__ :
__Encoding Type__ :
This field uses 2 lowest bits of first byte, describing 4 different block types :
| Value | 0 | 1 | 2 | 3 |
| ---------- | ---------- | ------ | --- | ------- |
| Block Type | Compressed | Repeat | Raw | RLE |
| Value | 0 | 1 | 2 | 3 |
| ---------- | --- | --- | ---------- | ----------- |
| Block Type | Raw | RLE | Compressed | RepeatStats |
- Compressed : This is a standard huffman-compressed block,
starting with a huffman tree description.
@@ -764,14 +764,14 @@ Literal Lengths, Offsets and Match Lengths respectively.
They follow the same enumeration :
| Value | 0 | 1 | 2 | 3 |
| ---------------- | ------ | --- | ------ | --- |
| Compression Mode | predef | RLE | Repeat | FSE |
| Value | 0 | 1 | 2 | 3 |
| ---------------- | ------ | --- | ---------- | ------ |
| Compression Mode | predef | RLE | Compressed | Repeat |
- "predef" : uses a pre-defined distribution table.
- "RLE" : it's a single code, repeated `nbSeqs` times.
- "Repeat" : re-use distribution table from previous compressed block.
- "FSE" : standard FSE compression.
- "Compressed" : standard FSE compression.
A distribution table will be present.
It will be described in [next part](#distribution-tables).